My grandmother urinates in the kitchen sink

Hey everyone. I’m Davey & I’m 20 years old. My grandmother is 78, and for the past year I’ve caught her urinating in the sink. This morning I caught her again, and asked why does it keep continuing. Well, she gave me the whole “you didn’t see anything, your an a**hole who’s just mean to me” the whole 9 yards. The thing that gets me is, she takes the lazy route of urinating in cups, and pouring it down the sink, when she goes upstairs all day long to make the bed, put clothes away & such. She has bad arthritis in her legs & back, but this does not make it okay to urinate in the kitchen sink where the dishes are washed daily. This morning I just went OFF. I mean F words from here to China. The reason being I try to talk to her like a human being, and have her explain to me why it keeps happening & she just talks to me like I’m 9 years old and says I’m picking on her (believe me, I’m not). The kitchen sink has taken on such a putrid urinal smell I can’t even go in there without gagging. This is literally the 25th time I’ve seen her doing this. I know the whole “well, you’re 20 move out” and trust me, it’s easier said than done. Me, my mom & step dad are moving into our own house in a month or so’s time. This has just got to stop, I think that’s why I lost my cool this morning. The last time I caught her, me & my mother sat down with her & explained how wrong it is to be doing this, and i thought it was over, but she just KEEPS doing it. Why Yahoo? Why does she keep pouring urine down the sink when she knows it wrong? It makes me wonder sometimes if she really is “losing it” because if a stranger came in & saw how truthful she sounds saying she doesn’t do it, they’d think I was lying. I don’t know if she’s really believing what she is saying. She knows she doing this, but she’d never admit to it. So Yahoo, what needs to be done? This is a very serious question. Please help me, I’m at wits end & I just want it to stop, & I’d be willing to help her with whatever problem that keeps her urinating in cups & emptying them into the sink. Thank you, & have a great day guys, Davey.